甘肃礼县李坝大型金矿床成矿地质特征及成因

Geology and Metallogenesis of Liba Large-size Gold Deposit in Lixian, Gansu Province

文章以成矿地质条件、矿床地质特征为基础 ,通过Ar_Ar年龄测定、稳定同位素测试和地层含金性分析等 ,研究了李坝金矿床的成因。研究表明 ,李坝金矿床与中川花岗岩在时间、空间和成因上关系密切。含金石英脉Ar_Ar法、Rb_Sr法和Pb_Pb法年龄为 2 10～ 171.6Ma ,与中川岩体年龄 (177～ 2 2 9Ma)吻合。包裹体水的δD - 74‰～ - 83‰ ,δ18O水 9.5 1‰～ 11.72‰ ,成矿流体水为岩浆水和大气降水的混合水。花岗岩提供了部分成矿物质来源 ,含矿热液通过F1导矿构造进入F3 、F12

Based on an analysis of the geology and metallogenic characteristics, combined with Ar-Ar dating,isotope analysis and Au determination, the authors have studied the metallogenesis of the Liba gold deposit. Ar-Ar dating, Rb-Sr dating and Pb-Pb dating yield the ore-forming age of 210 Ma～171.6 Ma, consistent with the age of the Dashan granite. According to H and O isotope analysis, δD values range from -74‰ to -83‰ averaging -79.88‰. δ 18O water values vary between 9.51‰ and 11.72‰, averaging 10.66‰. It is held that the ore-forming fluid was mainly derived from magmatism and heated underground water. Statistics on Devonian sediments in western Qinling orogeny gives the background Au value of 2.9×10 -9. Nevertheless, the background Au value of Mid-Upper Devonian sediments in Lixian-Minxian area where the Liba gold deposit is located is 4.7×10 -9, higher than Au values of the sedimentary cover and the upper crust of the West Qinling Mountains. Shujiaba Formation provided favorable source beds for Au mineralization. It is also considered that the Liba gold deposit is a by-product of Zhongchuan granite which provided heat source and main partial water source for Au mineralization, that the solution was in return heated by deep granite and circulated in Devonian sediments to form ore-forming solution. In structure, F 1 acted as a passage conduit through which ore-forming solution entered such ore-hosting structures as F 3 and F 12 for the deposition of Au.